The first important thing to bear in mind to use a current limiting resistor at base.
Pnp transistor high side switch.
Npn transistor as a switch.
We ll need a more complex circuit to implement a practical high side power on switch.
The application of an pnp transistor is to work as a high side switch.
Which means that pnp transistor shown in the first image will always be on regardless of the i o pin state.
Both npn and pnp transistors can be used as switches.
Higher base currents will damage a bjt.
Alternatively we can use a pnp transistor to create a high side switch.
A transistor has a 3 sandwich.
Npn high side switch r2 works as a pullup resistor to keep the base positive when the npn is off so that the pnp is off too.
This time however the emitter is tied high.
Trans istor transistor the prefix trans tells about signal transfer from low resistance to high resistance part and istor means solid physical structure having property of resistance.
Similar to the npn circuit the base is our input and the emitter is tied to a constant voltage.
The opposite of the low side switch is the high side switch.
It has three terminals named as base emitter and collector.
Transistor as switch.
Notice that the emitter is connected to the positive voltage.
The arrow in the emitter of a pnp transistor points in the opposite direction than in an npn transistor.
When npn turns on it sinks current through r1 r2 and this creates a voltage drop to the base of pnp which turns it on.
The real switch is still the pnp transistor on the right.
Transistor is 3 terminal electronic semiconductor component device.
I normally would switch the high side second diagram but i guess the first method should also work although it would dissipate more power in the transistor and not have.
Some of the applications use a power transistor as switching device at that time it may necessary to use another signal level transistor to drive the high power transistor.
Transistor name meaning lies in its own working.
I saw a suggestion on using a pnp for switching a load on the low side with the collector grounded emitter following the input first diagram as opposed to the high side.
This transistor connects between v and the load.
Figure 8 2 shows a circuit using a pnp transistor as a high side switch.
To explain with a pspice model pn2907a transistor has been selected.
Typically these use a pnp bjt or p channel mosfet.
The circuit above is called a low side switch because the switch our transistor is on the low ground side of the circuit.
